Hi.
The length of time someone will remain high is hard to predict--it depends on your body metabolism, the strength of the marijuana, and other factors. However, people usually report that their marijuana high lasts anywhere from 45 minutes to 3 hours.
It may be possible for you to hide the fact that you are high by trying to "hold it together" when you are around your parents or teachers, but there is no guarantee that they won't notice the typical signs--bloodshot eyes, frequent laughter, and an all-around change in behavior.
You've probably heard your friends describe the pleasurable feelings they experience when getting high, or thought it looked like fun, but it's probably best for you to get the other side of the story before you make the decision.
Pot is potentially addictive. Whether you become addicted or not depends on a variety of factors, so it's often not predictable who will and will not become dependent. Some people are able to smoke once in a blue moon and others feel compelled to smoke every few hours.
You should also be aware of the not-so-pleasant side effects. Some people experience a feeling of anxiety or paranoia when high. Some--especially those who smoke a lot--tend to withdraw socially, have trouble concentrating, or feel a general lack of motivation. And, as with any type of smoking, taking and holding smoke in your lungs may put you at increased risk for lung cancer.
Take care.
